Adding experimental IWebDriver extension methods to .NET support classes

This commit adds extension methods to IWebDriver, which can be used to
reduce the amount of type casting that must be done to access
functionality not provided by the base IWebDriver interface. The following
methods were added:

 * TakeScreenshot() - does not require a cast to ITakesScreenshot, and has
   support for working directly with instances of RemoteWebDriver.
 * ExecuteJavaScript<T>() - does not require a cast to
   IJavaScriptExecutor, and will automatically cast the result to the type
   specified by the generic type parameter (T).

These extension methods should be considered experimental. To use them
requires a reference to WebDriver.Support.dll, and adding a using clause
for OpenQA.Selenium.Support.Extensions.

dotnet/src/support/Extensions/WebDriverExtensions.cs

@@ -0,0 +1,97 @@
+// <copyright file="WebDriverExtensions.cs" company="WebDriver Committers">
+// Copyright 2013 Software Freedom Conservancy
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Text;
+using OpenQA.Selenium.Remote;
+
+namespace OpenQA.Selenium.Support.Extensions
+{
+    /// <summary>
+    /// Provides extension methods for convenience in using WebDriver.
+    /// </summary>
+    public static class WebDriverExtensions
+    {
+        /// <summary>
+        /// Gets a <see cref="Screenshot"/> object representing the image of the page on the screen.
+        /// </summary>
+        /// <param name="driver">The driver instance to extend.</param>
+        /// <returns>A <see cref="Screenshot"/> object containing the image.</returns>
+        /// <exception cref="WebDriverException">Thrown if this <see cref="IWebDriver"/> instance
+        /// does not implement <see cref="ITakesScreenshot"/>, or the capabilities of the driver
+        /// indicate that it cannot take screenshots.</exception>
+        public static Screenshot TakeScreenshot(this IWebDriver driver)
+        {
+            ITakesScreenshot screenshotDriver = driver as ITakesScreenshot;
+            if (screenshotDriver == null)
+            {
+                IHasCapabilities capabilitiesDriver = driver as IHasCapabilities;
+                if (capabilitiesDriver == null)
+                {
+                    throw new WebDriverException("Driver does not implement ITakesScreenshot or IHasCapabilities");
+                }
+
+                if (!capabilitiesDriver.Capabilities.HasCapability(CapabilityType.TakesScreenshot) || !(bool)capabilitiesDriver.Capabilities.GetCapability(CapabilityType.TakesScreenshot))
+                {
+                    throw new WebDriverException("Driver capabilities do not support taking screenshots");
+                }
+
+                MethodInfo executeMethod = driver.GetType().GetMethod("Execute", BindingFlags.Instance | BindingFlags.NonPublic);
+                Response screenshotResponse = executeMethod.Invoke(driver, new object[] { DriverCommand.Screenshot, null }) as Response;
+                if (screenshotResponse == null)
+                {
+                    throw new WebDriverException("Unexpected failure getting screenshot; response was not in the proper format.");
+                }
+
+                string screenshotResult = screenshotResponse.Value.ToString();
+                return new Screenshot(screenshotResult);
+            }
+
+            return screenshotDriver.GetScreenshot();
+        }
+
+        /// <summary>
+        /// Executes JavaScript in the context of the currently selected frame or window
+        /// </summary>
+        /// <typeparam name="T">Expected return type of the JavaScript execution.</typeparam>
+        /// <param name="driver">The driver instance to extend.</param>
+        /// <param name="script">The JavaScript code to execute.</param>
+        /// <param name="args">The arguments to the script.</param>
+        /// <returns>The value returned by the script.</returns>
+        /// <exception cref="WebDriverException">Thrown if this <see cref="IWebDriver"/> instance
+        /// does not implement <see cref="IJavaScriptExecutor"/>, or if the actual return type
+        /// of the JavaScript execution does not match the expected type.</exception>
+        public static T ExecuteJavaScript<T>(this IWebDriver driver, string script, params object[] args)
+        {
+            IJavaScriptExecutor executor = driver as IJavaScriptExecutor;
+            if (executor == null)
+            {
+                throw new WebDriverException("Driver does not implement IJavaScriptExecutor");
+            }
+
+            object result = executor.ExecuteScript(script, args);
+            if (!result.GetType().IsAssignableFrom(typeof(T)))
+            {
+                throw new WebDriverException("Script returned a value, but the result could not be cast to the desired type");
+            }
+
+            return (T)result;
+        }
+    }
+}

dotnet/src/support/WebDriver.Support.csproj

@@ -75,6 +75,7 @@
     <Compile Include="Events\WebDriverNavigationEventArgs.cs" />
     <Compile Include="Events\WebDriverScriptEventArgs.cs" />
     <Compile Include="Events\WebElementEventArgs.cs" />
+    <Compile Include="Extensions\WebDriverExtensions.cs" />
     <Compile Include="GlobalSuppressions.cs" />
     <Compile Include="PageObjects\ByChained.cs" />
     <Compile Include="PageObjects\ByFactory.cs" />